This invention relates generally to microwave devices and more particularly to microwave magnetically tuned devices which can be integrated with microwave monolithic integrated circuits.
As is known in the art, so-called monolithic microwave, and millimeter wave integrated circuits include active and passive devices which are formed using semiconductor integration circuit techniques to provide various types of microwave and millimeter wave circuits. In particular, monolithic microwave integrated circuits which include field effect transistors, transmission lines, resistors, and capacitors may be interconnected to provide various microwave circuits such as amplifiers, filters, switches, and the like. Such monolithic microwave integrated circuits are generally fabricated on materials such as gallium arsenide which have generally accepted characteristics which make their performance suitable at microwave frequencies.
Two types of microwave devices which are commonly employed in the art are so-called band reject filters and switches.
Band reject filters, are frequently used in electronic counter measurement systems (ECM), as well as, electronic support measures systems (ESM), particularly in receiver channels to suppress a strong signal in a certain frequency band, when it is desired to detect and process other signals particularly weaker signals located in adjacent frequency bands. Such filters are also commonly employed in certain radar systems to isolate the radar receiver path from a transmitted signal during radar transmission particularly when the transmitter and receiver share a common signal path. Commonly, a tuneable band pass filter is employed in such radar systems and during transmission it is detuned from the frequency of the transmitted signal.
Generally, the filters described above include YIG-sphere resonators that are tuned by means of an externally applied magnetic field. Several disadvantages occur with the use of YIG tuned resonators. A significant disadvantage is that although YIG filters have been built using photolithographic techniques, the requirement of the orientated YIG sphere, as well as, difficulty with electromagnetic coupling to the sphere make such magnetically tuneable devices based upon YIG sphere resonators not readily integratable with semiconductor circuits. Furthermore, if the filter has to operate at relatively high microwave or millimeter wave frequencies typically above 20 GHz, for example, a very large magnetic field is required to provide the requisite resonant circuit. At 20 GHz, it becomes very difficult to provide a large magnetic field in a package of small, acceptable size in applications where size is important.
Accordingly, a magnetically tuned circuit which may be fabricated using semiconductor integration circuit techniques and which may be directly integrated with such integrated circuits would be desirable. Further, circuits which operate at lower magnetic field strengths and which are also compact would also be desirable.